noarch and custom icons

### Checklist

- [x] I added a descriptive title
- [x] I searched open requests and couldn't find a duplicate

### What is the idea?

Menuinst supports creating shortcuts for noarch packages (see [this documentation](https://conda.github.io/menuinst/conda/#adding-shortcuts-to-conda-packages)), but it doesn’t appear to handle custom icons.

As we discussed during the transition to noarch ([see this issue comment](https://github.com/conda-forge/mss-feedstock/pull/198#issuecomment-3251697985)), we're unsure how custom icons are typically managed. Currently, we use `bld.bat` and `build.sh` scripts to copy the icon files to their final destination.

Is there a standard naming convention or another mechanism within menuinst that would allow us to automatically copy these icons without relying on custom build scripts?

### Why is this needed?

building a noarch package with custom icons

### What should happen?

by a naming convention for icons the icons get copied without a bld.bat or build.sh to the right directory. This should be documented.

### Additional Context

_No response_

Start with the linked menuinst noarch shortcut documentation and compare how bld.bat and build.sh currently copy custom icon files. Determine whether menuinst has an existing convention or mechanism for locating and copying icons, then document the agreed naming convention and verify that noarch packages install the icons without custom build scripts.

Written by the indexing model from the issue text.